This invention relates to apparatus and method for protecting devices in hostile environments. It has particular relevance for protecting optical fibre cables, transducers and components in oil, gas and geothermal wells.
In the normal production of oil and gas it is recognised that accurate and detailed information of the pressure and temperature in the oil and gas wells is important in order that adjustments can be made to flow rates and in order that preventive action can be taken to remedy damaging or potentially damaging conditions in the well. Similarly it is common practice for operators to stop the well from producing periodically, in order to observe the rate at which the downhole pressure changes after flow has been stopped. Accurate recording of the pressure profile provides the operator with valuable information regarding the condition of the well assembly and the condition of the region in the reservoir near the producing section of the well. The variation of the pressure during the period following cessation of production also helps to establish the physical extent of the region in the reservoir which is in pressure communication with the well. Furthermore, when electrical pumps are installed in oil wells in order to assist and speed up the rate of production, the knowledge of pressure and temperature along the pump is useful in adjusting the pump operating conditions such that undesirable conditions are avoided which can lead to damage to the pump assembly because repair and replacement can be extremely expensive.
Pressure sensors and temperature sensors are commercially available which are capable of being installed in the difficult conditions encountered in many oil and gas wells. Commonly used sensors are ones based on quartz transducers or silicon strain transducers. Such sensors generally have active electronic modules associated with them that must be located very near the transducers. Electrical cables then link the sensing assembly to the surface, providing electrical power for the sensor assembly and transmission of the sensor signal. It is well known that as oil is produced from deeper reservoirs, the downhole temperature and pressure increases and the sensor and sensor electronics have to survive under increasingly difficult conditions. The conditions are made all the more difficult as the surrounding environment contains water and many other reactive chemicals which react with the sensor assembly. Temperatures are often higher than 100 degrees Centigrade and can reach 200 degrees C or higher. Pressures encountered are often in excess of 10,000 psi and can exceed 20,000 psi.
Oil companies frequently have experienced failures of sensors under such conditions, sometimes within very short periods after installation and often within one or two years. Replacement of failed sensors or the associated cables and connectors is often economically impractical since it involves the shut-down of the well and requires expensive procedures to extract the sensor system from the well and to replace it.
Optical fibre sensors have been developed in order to overcome the short-comings of electronic sensors such as silicon based or quartz based gauges. Optical fibre gauges are passive devices that do not require active electronic assemblies near the measurement point. Generally optical fibres used for such purposes are made of silica which has a melting point near 2000 degrees Centigrade and which has many excellent engineering qualities. It is a very elastic material, with a very low coefficient of thermal expansion and remains elastic at pressures as high as 20,000 psi or greater. During the manufacturing process, optical fibres are coated with a protective material to prevent chemical attack of the silica which results in weakening of the fibre.
SensorDynamics has developed a fibre optic pressure sensor assembly consisting of a polariser, a pressure sensitive sidehole fibre and a mirror, all fusion spliced to an optical fibre lead. Such pressure sensors have been shown to have excellent performance features such as linearity, high resolution and survival at temperatures above 300 degrees C and at pressures in excess of 15,000 psi.
These sensors have a further and very important advantage derived from the fact that they are typically very thin and flexible. Optical fibres are typically between 100 microns and 500 microns in diameter, hence can be simply joined to optical fibre cables of similar diameter and can be deployed over many kilometres through hydraulic control lines using fluid drag. Hydraulic control lines typically have outside dimensions of xc2xc inch and are frequently a feature of oil and gas wells and are used to control valves and chokes and also to inject chemicals or gas to assist the efficient production of reservoir fluids. More recently hydraulic control lines have been included in the construction of oil wells in order to provide a conduit through which optical fibre cables and sensors can be transported to the remote regions of the oil or gas well in order to acquire pressure, temperature and potentially other information. The ability to deploy sensors over long distances is important for many reasons. It removes the need for complicated electrical connectors or optical connectors in difficult locations along the well construction, allows different types of sensors to share the same control line conduit, allows other sensors to be added to the same network without interrupting the normal operation of the oil or gas well and, in the event of a sensor failure, makes replacement of sensor and cable practical and economically acceptable and recalibration possible and simple.
Whereas the optical fibre pressure sensors have displayed these excellent characteristics described above, they have all exhibited a rapidly changing zero point when exposed to a high temperature, high pressure environment which contains water in liquid phase, forming either the major component of the liquid material, or as a dissolved component in another liquid material. This zero point instability has been investigated extensively and it has been established that the rate of drift of the zero point is greater at higher temperatures and is faster when the pressure sensors are surrounded by water than if immersed in another fluid such as silicone and polysiloxane oils (such as Syltherm 800 Heat Transfer Liquid supplied by Univar plc) have shown that the drift of the zero point is caused by ingress of water or OH radicals into the silica body of the optical fibre, resulting in a highly stressed layer which starts to form at the surface of the optical fibre sensor and gradually extends inward. This stress layer has been shown to form in coated fibres as well as in uncoated silica fibres. Carbon coatings have been shown to slow down the formation of the stress layer. Stress layers alter the response of pressure sensors significantly and mask the true variation of pressure in the well. Where an in-fibre Bragg grating has been used as a pressure transducer, this drift has been shown to be as high as 30,000 psi, after a period of a few weeks or months, when exposed to water at 250xc2x0 C. and 5000 psi pressure. In the case of a polarimetric sensor the change has been significantly lower but still resulted in a zero drift of 6000 psi under similar environmental conditions. Further measurements were carried out on commercially available, optical fibres and have established that the ingress of OH radicals causes the significant increase in the physical length and in the optical length of the fibres. Clowes et al. (see Electronics Letters, May 27th 1999, pages 926 to 927) reported changes greater than 0.1% in the physical length. Again it was found that carbon coatings that were developed to provide hermetic protection, to prevent the ingress of hydrogen into optical fibres employed in subsea communications cables, also reduce the rate at which the effect occurs. It has also been shown that no polymer coatings have been able to prevent the ingress of OH at 250xc2x0 C. and 4000 psi in the presence of water. In many cases where coated, or uncoated fibres were exposed for periods of weeks or months, to fluids at high temperature and pressure, particularly under field test conditions it was observed that irregular solid deposits formed on the outside surface of the fibre structure. Sensors have also been shown to drift when immersed in polysiloxane oil and alcohols, but at less than 10% of the rate with water. Nonetheless, this drift rate is considered unacceptable for the accurate acquisition of downhole pressure data.
These observations have established that if optical fibres are to survive long-term at high temperatures and pressures in the presence of water, then it is essential to coat these fibres with a hermetic material which can block ingress of OH (or other molecules (methanol etc)) into silica under these conditions.
No polymer materials are known to us that can claim to provide such protection. Carbon coatings have proved their value under less extreme conditions and are known to provide long term protection for telecommunications optical cables which may be used in subsea links. Carbon coated optical fibres and fibre sensors have been tested under the more demanding conditions encountered in oil and gas production where they have shown moderate improvements, but have failed to achieve the degree of protection required by pressure sensors which are intended for use in hot, high pressure oil and gas wells. Metallic coatings such as gold, copper, tin have been shown to be hermetic. Metal coatings also promise the advantage over carbon, in that they are able to survive bending of the fibre without cracking which can lead to a breakdown of the hermetic seal. Metals are also able to survive at high temperatures. However, when coatings are to be used to protect pressure sensors, then the relatively high thermal coefficient of expansion of metals makes the pressure sensor more sensitive to changes in temperature. Furthermore, chemical reactions between the surrounding environment and the solid metal coating can also lead to a change in the stress and therefore can cause a change in the zero offset of the pressure sensor and therefore to a false indication of the pressure.
A solution that provides protection for optical fibres, optical fibre transducers and optical fibre components in oil, gas and geothermal wells may have widespread application for protecting other devices in hostile environments and may have general application in ensuring that different fluids do not mix. Hostile environments can be considered to be those environments that affect the performance and reliability of devices, especially optical and fibre-optic devices. Hostile environments are found in many process industries such as refineries, food processing, wood pulp processing, pharmaceutical production and the nuclear power industry. They are often characterised by high temperatures, high pressures and the presence of corrosive and/or aggressive fluids. An example of a highly-corrosive fluid is water at high temperatures and pressures (200C and 4000 psi). High-temperature water is found in many industrial processes.
The aim of this invention is to provide apparatus and method for protecting devices in hostile environments. A further aim is to improve the stability of sensors that are exposed to conditions of high temperature and pressure in the presence of hostile fluids, particularly fluids that may be encountered in downhole applications.
According to a non-limiting embodiment of the present invention, there is provided apparatus for protecting an optical device from a hostile environment, which apparatus comprises the optical device and a liquid wherein the liquid substantially surrounds the optical device.
The optical device can be selected from the group consisting of a transducer, a cable, an optical fibre cable, a region disposed about a splice in a cable, a region disposed about a splice between a cable and a transducer.
The liquid can be selected from the group consisting of liquid metal, gel, inks, grease and oil.
The grease can contain lithium, molybdenum, or synthetics, or be synthetic grease.
The liquid metal can be selected from the group comprising mercury, gallium, indium, an alloy that includes indium and gallium, an alloy that includes indium and tin, an alloy that includes indium and bismuth, an alloy that includes gallium and tin, an alloy that includes gallium and bismuth, and an alloy that includes cadmium.
The ink can be a thin-film commercial ink such as an ink used in thick-film hybrid electronic circuit manufacture.
The liquid can contain other components such as a scavenger or getter for molecules and/or ions.
The apparatus can include a first container wherein the liquid is substantially contained within the first container. The first container can be a sealed container. The first container can be a capillary.
The apparatus can include a first and second container. The first container may be substantially contained within the second container. The second container can contain a second liquid or a second fluid. The second liquid may be the same material as the liquid surrounding the optical device.
In a preferred embodiment of the invention, there is provided apparatus for protecting an optical device from a hostile environment, which apparatus comprises the optical device, a liquid, a cable and a capillary, wherein the optical device is an optical fibre sensor connected in series with the cable.
The cable can be an optical fibre cable, the liquid can be gallium, the optical device can be an optical fibre sensor packaged inside a capillary containing the gallium. The capillary can extend over any splice region between the optical fibre sensor and the optical fibre cable, and the gallium preferably surrounds both the splice region (if present) and the optical fibre sensor.
The optical device can be a plurality of optical fibre sensors substantially surrounded by one or more liquids. The optical fibre sensors can be contained in at least one capillary.
The optical fibre sensor can be selected from the group consisting of an optical fibre pressure sensor, an optical fibre acoustic sensor, an optical fibre temperature sensor, an optical fibre seismic sensor, a distributed optical fibre temperature sensor, a distributed optical fibre pressure sensor, an optical fibre flow sensor, and an optical fibre sensor comprising at least one optical fibre Bragg grating.
In a second embodiment of the invention, there is provided apparatus for protecting a transducer from a hostile environment comprising the transducer and a liquid wherein the liquid substantially surrounds the transducer.
The transducer can be an optical transducer or can be an electrical transducer. The electrical transducer can be a pressure gauge such as a quartz pressure gauge used in downhole applications in the oil and gas industry.
The transducer can be an optical fibre sensor.
The transducer may be connected to a cable.
The liquid can be a liquid metal. The liquid metal can be gallium.
The liquid metal may be selected from the group comprising mercury, indium, an alloy that includes indium and gallium, an alloy that includes indium and tin, an alloy that includes indium and bismuth, an alloy that includes gallium and tin, an alloy that includes gallium and bismuth, and an alloy that includes cadmium.
The transducer can be packaged inside a first container wherein the liquid is substantially contained within the first container. The first container can be a sealed container.
The first container can be a first capillary that may be flexible. The first capillary may be substantially contained within a second capillary. The second capillary can contain a second liquid. The second liquid may be selected from the group consisting of a liquid metal, silicone oil, siloxane oil, polysiloxane oil, hydrocarbon oil, hydrocarbon fluid, grease and a gel.
In another aspect of the invention an optical device is protected from a hostile environment by a liquid substantially surrounding the optical device.
The optical device can be a transducer. The transducer may be installed in an oil, gas or geothermal well or other harsh environment.
The transducer can be an optical fibre transducer that may be connected in series with an optical fibre cable.
The liquid is a liquid metal selected from the group comprising gallium, indium, an alloy that includes indium and gallium, an alloy that includes indium and tin, an alloy that includes indium and bismuth, an alloy that includes gallium and tin, an alloy that includes gallium and bismuth, and an alloy that includes cadmium.
A capillary can be provided to contain the liquid and the optical fibre transducer which may be a pressure sensor.
Another aspect to the invention provides an optical fibre cable comprising an optical fibre, a liquid and a capillary wherein the optical fibre is contained within the capillary and the liquid surrounds the optical fibre.
The liquid can be selected from the group consisting of liquid metal, gel, inks, grease and oil.
The grease can contain lithium, molybdenum, or synthetics, or be synthetic grease.
The liquid metal can be selected from the group comprising gallium, indium, an alloy that includes indium and gallium, an alloy that includes indium and tin, an alloy that includes indium and bismuth, an alloy that includes gallium and tin, an alloy that includes gallium and bismuth, and an alloy that includes cadmium.
Another aspect to the invention provides an optical fibre splice comprising a first optical fibre, a second optical fibre, a fusion splice, a capillary and a liquid wherein the first and the second optical fibres are connected together at the fusion splice, and wherein the liquid surrounds the fusion splice and wherein the capillary contains the liquid around the fusion splice.
The liquid can be selected from the group consisting of liquid metal, gel, inks, grease and oil.
The grease can contain lithium, molybdenum, or synthetics, or be synthetic grease.
The liquid metal can be selected from the group comprising gallium, indium, an alloy that includes indium and gallium, an alloy that includes indium and tin, an alloy that includes indium and bismuth, an alloy that includes gallium and tin, an alloy that includes gallium and bismuth, and an alloy that includes cadmium.
Another aspect to the invention provides a transducer comprising an optical fibre transducer, a liquid and a capillary wherein the capillary contains the liquid and wherein the liquid surrounds the optical fibre transducer.
The liquid can be selected from the group consisting of liquid metal, gel, inks, grease and oil.
The grease can contain lithium, molybdenum, or synthetics, or be synthetic grease.
The liquid metal can be selected from the group comprising gallium, indium, an alloy that includes indium and gallium, an alloy that includes indium and tin, an alloy that includes indium and bismuth, an alloy that includes gallium and tin, an alloy that includes gallium and bismuth, and an alloy that includes cadmium.
A preferred embodiment of the present invention is an optical device placed in an oil, gas or geothermal well.
The oil, gas or geothermal well may contain a conduit extending from the surface to a measurement location. The optical device may be a transducer or an optical fibre cable.
The transducer may be connected in series with an optical fibre cable. The optical fibre cable and the transducer may be located within the conduit. The transducer may be located within the conduit by pumping the transducer along the conduit.
The invention also provides a method and an apparatus for separating two fluids by an interposing liquid. The interposing liquid may be a liquid metal.
The liquid metal can be selected from the group comprising gallium, indium, an alloy that includes indium and gallium, an alloy that includes indium and tin, an alloy that includes indium and bismuth, an alloy that includes gallium and tin, an alloy that includes gallium and bismuth, and an alloy that includes cadmium.
This embodiment is particularly attractive for communicating pressure between a first port and a second port or for segregating various sensing segments of a single highway. By highway we mean a conduit through which sensors and cables can be pumped, especially to remote locations such as found within oil, gas and geothermal wells. The conduit can be hydraulic steel control line, titanium control line, coiled tubing or other pipes and tubes which are used in the oil and gas industry. The conduit can also be ceramic tubing, plastic tubing, or tubing constructed from other materials such as synthetics.
The embodiment can be an apparatus for measuring pressure comprising a first port, a liquid metal and a pressure sensor in which the liquid metal transfers pressure from the first port to the pressure sensor.
The apparatus can comprise a first chamber, a pressure sensor, a capillary and a liquid metal, in which the pressure sensor is contained in the first chamber, which is connected to the location where pressure is to be measured by the capillary and the liquid metal.
The first chamber can contain an oil that may be chosen from the group silicone oil and polysiloxane oil.
The first chamber may contain a liquid metal.
The capillary may contain a liquid metal.
The liquid metal can be selected from the group comprising gallium, indium, an alloy that includes indium and gallium, an alloy that includes indium and tin, an alloy that includes indium and bismuth, an alloy that includes gallium and tin, an alloy that includes gallium and bismuth, and an alloy that includes cadmium.
The apparatus may include a second chamber and a port to the measurement location. The second chamber may contain a liquid metal.
Another aspect to the invention provides a mirror formed on an optical fibre comprising the optical fibre and a liquid metal wherein the optical fibre has a cleaved end face and wherein the liquid metal is in contact with the cleaved end face of the optical fibre.
The liquid metal can be selected from the group comprising gallium, indium, an alloy that includes indium and gallium, an alloy that includes indium and tin, an alloy that includes indium and bismuth, an alloy that includes gallium and tin, an alloy that includes gallium and bismuth, and an alloy that includes cadmium.
Another embodiment of the present invention provides a sensor element comprising a transducer, a liquid coating and a container means for containing the liquid coating.
The liquid coating may be a liquid hermetic coating which reduces or prevents the ingress of molecules or ions such as water or OH groups, or hydrogen, into the silica of the optical fibre sensor.
The container means may be a capillary or any other form of container which ensures that the liquid coating remains in contact with the transducer. The container means may be made from a flexible material such as PTFE. It may be that the preferable container should be fabricated from silica in the form of a silica capillary, the dimensions of which are such that the total transducer package is flexible and deployable in the xc2xcxe2x80x3 inch hydraulic control line. It is known that hermetic carbon coatings can be deposited onto silica fibres (and hence capillaries) during the drawing fabrication process. This provides an additional protection to the transducer package.
An additional benefit of the use of silica as the transducer and liquid container is that the physical bonding of the container to the silica fibre itself can be easily achieved through thermal fusion of the silica capillary to the silica fibre (a process commonly used in splicing of silica optical fibres). Other methods of physically bonding the capillary to the silica fibre include; the use of an adhesive, a metal with a melting point which is higher than the ambient temperature at which the sensor or cable is to be used or the formation of a mechanically strong bond between the capillary and the fibre through a process of tapering of the capillary to produce a narrow bore and hence close fit between capillary and the contained fibre.
The capillary may be open at the top or may be open at the bottom. Alternatively it may be closed at both ends.
The sensor element may be connected to an optical fibre cable which may be enclosed along the entire length (downhole) in the capillary in which case the capillary to fibre seal may be external to the oil well and securely sealed against pressure. The advantage of this approach is that the entire package may be of such dimensions that it may be placed inside a stainless steel control line and may be pumped to its measurement location and/or retrieved to the surface using fluid drag. Also this design would provide an hermetic seal and provide mechanical protection along the whole length of the fibre. The sensor element may be an optical fibre sensor. The sensor element may be a pressure sensor, a temperature sensor or an acoustic sensor.
The pressure sensor may be a polarimetric pressure sensor constructed from side-hole fibre (J Clowes et al, Photonics Technology Letters Volume 10, 1998) or polarisation-maintaining fibre, or may be a pressure sensor based upon a variable air gap with a capillary around it, or may be a pressure sensor based upon an optical fibre Bragg grating.
The liquid coating may be a metal that is in the liquid state at the temperatures where measurements are to be carried out. The metal may be mercury, indium, gallium or lead. The metal may be an alloy which includes indium and gallium, or indium, gallium and tin, or indium, bismuth and tin, or bismuth, lead and cadmium, or silicon, lead, tin, cadmium and silver.
Any of the metals or alloys may have other compounds added which act as scavengers or getters for molecules or ions such as water or OH, or hydrogen, or others.
The liquid coating may be a grease. The grease may contain lithium, or a combination of lithium and molybdenum.
The grease may have compounds added which act as scavengers or getters for such molecules or ions as water, or OH groups, or hydrogen or others.
In an embodiment of the present invention, the sensor element is of such dimensions and structure that it may be placed inside a conduit. The conduit may be a hydraulic control line such as xc2xcxe2x80x3 hydraulic control line commonly used in the oil and gas production industry.
The conduit may be part of an apparatus for extracting at least one of oil and gas from below ground, which apparatus includes a well head, a production tubing, a conduit, a cable and a sensor element in which the sensor element comprises a transducer, a liquid coating and a container means for containing the liquid coating.
The sensor element and the cable may have been pumped along the conduit.